TOF Frequency — FRCA Primary MCQ
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Correct answer: E — 2 Hz and 0.5 seconds
The correct answer is E. Standard train-of-four stimulation delivers four supramaximal stimuli at 2 Hz, so successive stimuli are separated by 0.5 seconds. The elapsed time from the first stimulus to the fourth is therefore 1.5 seconds; describing this as a total train duration of 2 seconds is imprecise. During non-depolarising neuromuscular block, successive responses fade, and the amplitude of T4 relative to T1 gives the TOF ratio. A frequency of 1 Hz is associated with repeated single-twitch stimulation rather than TOF. Frequencies of 50 Hz and 100 Hz are tetanic stimulation patterns. A 5 Hz train is not the standard TOF pattern.
Reference: Goyal P, et al. Anaesthesia and neuromuscular disorders: what a neurologist needs to know. Practical Neurology. 2021;21:128–139. https://www.rcoa.ac.uk/sites/default/files/documents/2019-11/Guideline_standards_of_monitoring_anaesthesia_recovery_2015_final%20%281%29%20to%20be%20uploaded.pdf